EDIT: I've also done the same process with guruboolez' harpsichord sample (uploaded to the same thread). Looking at the spectrum (I know, its naughty ), the HF difference is mostly above 8 kHz. The spectrum of the violin sample also has most of this high frequency difference above 8 kHz.

Hopefully something useful can be gathered from this.

Not much, I think. If the substraction shows content in > 8kHz range only this only tells you that both encodes are different in this range, while they're very similar/identical below 8kHz, but you don't know if one encoder contains more energy in >8kHz band than the other. The difference could simply be caused by phase shift (probably oversimplified, but to get the idea)

You could gather more useful information from (CEP/Audition) frequency analysis of identical positions.

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Let's suppose that rain washes out a picnic. Who is feeling negative? The rain? Or YOU? What's causing the negative feeling? The rain or your reaction? - Anthony De Mello

I encoded guruboolez' violin sample with the standard 1.0.1 coder and nyaochi's uncoupled stereo coder. Then in CoolEdit, I did a mix paste and saved the differences in order to (informally) highlight the differences.

I don't think Dibrom would be too impressed with this stuff. Maybe you should back it up with a listening test of you own? I just don't want to see you get flamed.

I don't think Dibrom would be too impressed with this stuff. Maybe you should back it up with a listening test of you own? I just don't want to see you get flamed.

The point of the exercise is to pinpoint the differences that uncoupled stereo has over coupled stereo rather than to compare coders subjectively (ie. this coder sounds better than that one). I'm not making any claims here, but just doing a bit of detective work and seeing if stereo coupling really is the cause of HF boost in Vorbis.

I know it's bad (I even stated it that this is bad) but I don't have good ears and have trouble hearing these distortions so I need an empirical way of observing the differences that guruboolez and [proxima] are noticing in their listening tests. Hopefully Dibrom will pardon me on this.

The point of the exercise is to pinpoint the differences that uncoupled stereo has over coupled stereo rather than to compare coders subjectively (ie. this coder sounds better than that one). I'm not making any claims here, but just doing a bit of detective work and seeing if stereo coupling really is the cause of HF boost in Vorbis.

I know it's bad (I even stated it that this is bad) but I don't have good ears and have trouble hearing these distortions so I need an empirical way of observing the differences that guruboolez and [proxima] are noticing in their listening tests. Hopefully Dibrom will pardon me on this.

Fair enough. I suppose Guruboolez will provide the conclusive evidence in the form of a listening test soon anyway, I guess its nice to have some idea of what's going on in the mean time. Although, it still might not go over too well.

Fair enough. I suppose Guruboolez will provide the conclusive evidence in the form of a listening test soon anyway, I guess its nice to have some idea of what's going on in the mean time. Although, it still might not go over too well.

My choices are rather limited unfortunately and I'm unable to go into the Vorbis source code and try to tackle this HF boost problem by relying on subjective comments on quality only.

But we'll try kjoonlee's suggestion and see how it goes. If these corrupted samples are ABXable and distortions are similar in nature to the HF boost, then we've at least verified experimentally that stereo coupling has problems

It's quite a good idea actually. What I might do is take these differences, add them back to the original, and get some people with good ears to ABX them.

I think this is not useful because, in this manner, we are completely ignoring masking. I see no reason to abx a such sample. Maybe someone more expert can confirm my assumption.I remember some Musepack spectral analysis where original and encoded differ a lot visually, but all the quantization noise is perfectly masked and the files are not ABXable.

,Feb 12 2004, 01:02 AM] I think this is not useful because, in this manner, we are completely ignoring masking. I see no reason to abx a such sample. Maybe someone more expert can confirm my assumption.I remember some Musepack spectral analysis where original and encoded differ a lot visually, but all the quantization noise is perfectly masked and the files are not ABXable.

I sort of guessed it wouldn't be so simple.

Oh well, in that case, I give up on the HF boost problem. I guess there is little point in me trying to fix something I cannot hear that well.

I'll focus on the tonality problem in the Arche I sample which I can actually hear as well as pre-echo issues.

Let me add two samples available here. You can hear boosted close hi-hat cymbal in the 8823 sample with 1.0.1 -q4. The second sample is white noise created by CoolEdit. I suppose some of you disagree with the use of artificially created sample, but the problem with 1.0.1 -q4 is too obvious for me. I found the sample encoded by 1.0.1 -q4 totally different from the original. I'm not sure this sample exposes HF boost problem (or another problem?), but I believe it's a good material to improve Vorbis.

,Feb 11 2004, 11:02 PM] I think this is not useful because, in this manner, we are completely ignoring masking. I see no reason to abx a such sample. Maybe someone more expert can confirm my assumption.I remember some Musepack spectral analysis where original and encoded differ a lot visually, but all the quantization noise is perfectly masked and the files are not ABXable.

That's why you add in the original signal to the difference. That way you have the masker signals present at those time the difference signal would be masked. Just listening to the difference signal however would have the problem you mention. Right? But why not compare the uncoupled stereo with the "joint stereo" one directly. All other variables are constant right?

A listening may not help to fix the HF boost. I'm affraid one would need to dig deeply into the source until finds where the energy difference comes from.

Maybe in this case listening cannot help to resolve codec problems, we need a capable person who can understand the code and correct this problem. Anyway, due to the availability of hardware Vorbis players, i think that testing is still important because :- maybe we can suggest the newbies a best, "HA approved" version/128 kbps settings.- there is the chance to reduce HF boost with "small hacks" such as disabling stereo coupling.

I’m late, but I didn’t have much free-time this week (and internet access is a second problem too). I have performed the test yesterday, comparing: - RC3 (march 2002)- 1.01 (october 2003)- lossless coupling (Quantum Knot)- uncoupled encoder (Nyaochi)

According to the fact that uncoupled encodings at –q4 are a lot bigger than traditionnal vorbis encoder at the same setting, I also add an uncoupled encoder at lower setting. Nyaochi uncoupled at –q2 is close to average bitrate of 1.01/RC3 –q4, but slightly inferior. I’ve therefore tested fully uncoupled encoder at –q2,3 in order to measure the negative impact of a sub-efficient (uncoupled) channel coupling at ~128 kbps, compared to the same encoder, helped with channel coupling.

• uncoupled encoders are winning again, without any doubts.• full uncoupled encoder [FU] (Nyaochi) is clearly superior to lossless coupled [LC] (provided by Quantum Knot) vorbis encoder. FU was always better than LC, except on one sample – Mars: same notation. These results confirm [proxima]’s conclusions.• both uncoupled encoders are still suffering from noise or tonality difference. The problem is not fully corrected: there are still differences. It’s not awfully annoying, but it’s difficult to forgive at ~160 kbps...

• at ~128 kbps, 1.01 appears again as a complete loser, compared to RC3 (harpsichord is the exception again) and to FU –q 2,3. There are so much noise and imprecision with 1.01... In other words, 1.01 without coupling was always better than 1.01 with coupling!!! • But FU –q 2,3 is far from perfection: there are much more noise than with FU at –q 4. Noise isn’t the only difference. Other artifacts appeared (for example, acidity on Spagna, distortions on Brahms). And pre-echo reached an annoying level.• Therefore, there are no clear winner between RC3 –q4 and FU –q 2,3. On four samples, RC3 sounded better; on the four others, it was FU. Overall notation is in favor of RC3, but the difference is distorted by an approximate notation (with deliberately exaggerating contrasts).

The aim of testing lossless and uncoupled stereo is to probe the behaviour of the HF boost. I think from guruboolez and [proxima]'s tests, we can conclude that the lossy coupling (point) is having problems but is not the sole cause. We also see that uncoupled stereo is not perfect and still suffers from noise.

So perhaps, the uncoupling has only reduced the effect of the hiss but not totally removed it. That is, it hasn't made the problem go away or solved it, but only made it harder to detect. Hence I'm beginning to believe that we can rule out stereo coupling as the cause of HF boost. Digging into the source code of rc3 may provide new insight as well as nyaochi's focus on the noise companding in his 'Modest Tuning'.

I know there may be some other people on the Vorbis-dev mailing list who are saying 'I told you so', but hey, it never hurts to do some comprehensive listening tests to verify it.

Some notes for the test. I ranked my favorite 3 samples as well as 8 classical samples presented by guruboolez. The main purpose of this test is to evaluate aoTuV b1 -q4 compared with 1.0.1 official -q4, RC3 (March 2002) -q4, lossless coupling -q4, uncoupled stereo -q4/-q2.3, and my modest tuning -q4. Note that bitrates are not similar between these samples (LC -q4, UC -q4 and MTb2 -q4 is much higher than 128kbps.)

I failed to abx 2 samples because I was not familiar with classical samples and got tired.

Results:At a grance, the total score shows that MTb2 was the first. However, it was not so good because the average bitrate of MTb2 is too high (around 160-170kbps). On the other hand, aoTuV has a good cost-performance without bitrate inflation. Preecho problem (e.g., Harpsichord and Mandolins) seems to lower the score (preecho is not his main target of the tuning).

Just as the listening results of guruboolez and [proxima], 1.0.1 official ends up the last place. UC was better than LC.